As main prior art used for applying an apex to the outer peripheral surface of a bead ring, there are those described in the Japanese patent publication gazette Nos. S51-29551 and S61-6782. In the former, there are described that an apex is fed from its one end onto a rotating bead ring suspended by a pair of guide rolls, successively pressed against the peripheral surface of the bead ring by a pair of pressing rolls and applied thereto in annular fashion, that, in the way of application, the bead apex is pinched by a disc roll and a cone roll so as to spread from its inner edge toward its outer edge, that the leading end of the apex having revolved to a predetermined angle is detected and a rear end portion of the apex is cut to a predetermined length, that both end portions of the apex opening in V-shape are clamped by a splicing mechanism and drawn near to cause both cut end surfaces to bond together, after the apex is applied to the whole periphery of the bead ring, and so on.
In the latter, there is a description that a bead ring is held on the periphery of rotatable disc, an apex which is previously cut to a predetermined length is applied to the peripheral surface of the bead ring in annular fashion with rotation of the disc, both side portions of both ends of the apex are clamped by two pairs of clamps (pressing elements) in a state where both ends of the apex face to form a V-shaped gap therebetween, and a thrust force is applied to the clamps by a third mechanism, thereby pulling both V-shaped facing end portions of the apex into butting bond.
When a bead apex having a relatively slender triangular cross-section is applied annularly to a bead ring, a V-shaped gap is inevitably formed at a junction of the leading and rear ends of the apex since there is a difference between the inner circumferential length of the apex put in contact with the peripheral surface of the bead ring and the outer circumferential length thereof including its outer edge portion (tip portion). According to the abovementioned prior art, there are such problems in that the apex may shrink especially in its outer edge portion in the way from the time when it is drawn out to the time when its application to the peripheral surface of the bead ring is completed, which makes the V-shaped gap between the both ends the larger, since both ends of the apex are clamped by clamping tools and drawn near into butting bond after the apex is applied to the peripheral surface of the bead ring, and that the amount of deformation of the end portions of the apex for cancelling the V-shaped gap is locally so significant that the shape of the outer edge of the apex is liable to become irregular in the vicinity of the junction and a clamp mark of the clamps may be left at the junction. The size of the V-shaped gap is not always fixed and some are large and others are small, since the degree of shrinkage varies with viscosity of the apex rubber. When it is clamped for bonding by the abovementioned prior art scissors-type clamping tools which can effect only a limited movement but no free drawing movement directly responding to the size of the V-shaped gap, there is such a problem in that a large operational stroke of the clamping tools set in conformity with a large gap in order to avoid misjoint may cause over joint (excessive bond) for a small gap and a small operational stroke set in conformity with a small V-shaped gap may cause insufficient bond to leave a gap in the junction in case of a large gap, thereby disabling us from obtaining a good joint in any case.